Reciprocating drive for scanning a workpiece

ABSTRACT

A reciprocating drive system, method, and apparatus for scanning a workpiece are provided, wherein a motor comprising a rotor and stator operable to individually rotate about a first axis is operable to reciprocally translate the workpiece with respect to a stationary reference. A shaft rotatably driven by the rotor extends along the first axis, and a scan arm is operably coupled to the shaft, wherein the scan arm is operable to support the Workpiece thereon. Cyclical counter rotations of the shaft by the motor are operable to rotate the scan arm, therein scanning the workpiece through the ion beam along a first scan path, wherein the stator acts as a reaction mass to the rotation of the rotor. A controller is further operable to control an electromagnetic force between the rotor and the stator, therein generally determining a rotational position of the rotor and the stator.

REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of U.S. ProvisionalApplication Ser. No. 60/559,672 which was filed Apr. 5, 2004, entitledRECIPROCATING DRIVE SYSTEM AND METHOD and U.S. Provisional ApplicationSer. No. 60/569,338 which was filed May 7, 2004, entitled RECIPROCATINGDRIVE SYSTEM AND METHOD, the entirety of which are hereby incorporatedby reference as if fully set forth herein.

FIELD OF THE INVENTION

The present invention relates generally to translational scanningsystems, and more specifically to a system, apparatus, and method forcontrolling reciprocating transport of a workpiece to provide precisionscanning of the workpiece.

BACKGROUND OF THE INVENTION

In the semiconductor industry, various manufacturing processes aretypically carried out on a workpiece (e.g., a semiconductor wafer) inorder to achieve various results thereon. Processes such as ionimplantation, for example, can be performed in order to obtain aparticular characteristic on or within the workpiece, such as limiting adiffusivity of a dielectric layer on the workpiece by implanting aspecific type of ion. Conventionally, ion implantation processes areperformed in either a batch process, wherein multiple workpieces areprocessed concurrently, or in a serial process, wherein a singleworkpiece is individually processed. Traditional high-energy orhigh-current batch ion implanters, for example, are operable to achievean ion beam-line, wherein a large number of wafers may be placed on awheel or disk, and the wheel is spun and radially translated through theion beam, thus exposing all of the surface area of the workpieces to thebeam at various times throughout the process. Processing batches ofworkpieces in such a manner, however, generally increases the cost ofthe system, makes the ion implanter substantially large in size, andreduces system flexibility.

In a typical serial process, on the other hand, an ion beam is eitherscanned two-dimensionally across a stationary wafer, or the wafer istranslated in one direction with respect to a generally stationaryfan-shaped ion beam. The process of scanning or shaping a uniform ionbeam, however, generally requires a complex beam-line, which isgenerally undesirable at low energies. Furthermore, uniform translationor scanning of either the ion beam or the wafer is generally required inorder to provide a uniform ion implantation across the wafer. However,such a uniform translation and/or rotation can be difficult to achieve,due, at least in part, to substantial inertial forces associated withmoving the conventional devices and scan mechanisms during processing.

Alternatively, in one known scanning apparatus, as disclosed in U.S.Patent Application Publication No. 2003/0192474, the wafer is scanned intwo orthogonal dimensions with respect to a stationary “spot” ion beam,wherein the wafer is quickly scanned in a so-called “fast scan”direction and then slowly scanned in an orthogonal “slow scan”direction, thereby “painting” the wafer via a generally zigzag pattern.This two-dimensional scanning apparatus, however, utilizes direct driveactuators to linearly translate the wafer in the fast scan direction,wherein the transport velocity of the wafer in the fast scan directionis substantially limited due, at least in part, to significant inertialforces encountered during acceleration and deceleration of the wafer asthe direction of fast scan transport is periodically reversed. Largeinertial forces in the conventional apparatus are accordingly associatedwith a large reaction force at the direct drive actuator, wherein thelarge reaction force can ultimately lead to significant vibration of theapparatus, thus having a deleterious impact on the ion implantationprocess. Vibration may also pose a problem for nearby equipment, such aslithography equipment that is typically vulnerable to vibration.Furthermore, when the speed of the translation in the fast scandirection is limited in order to avoid vibration issues, processthroughput can be deleteriously impacted.

Therefore, a need exists for a system and apparatus for reciprocallyscanning a workpiece in two dimensions relative to an ion beam atsubstantially high speeds, wherein vibration from large inertial forcesis mitigated, and wherein the scanning of the workpiece is controlled inorder to uniformly process the workpiece.

SUMMARY OF THE INVENTION

The present invention overcomes the limitations of the prior art byproviding a system and apparatus that generally confines forcesassociated with reciprocally scanning a workpiece to various componentsaligned along a single axis, thus substantially limiting vibration toenable increased process speeds. Consequently, the following presents asimplified summary of the invention in order to provide a basicunderstanding of some aspects of the invention. This summary is not anextensive overview of the invention. It is intended to neither identifykey or critical elements of the invention nor delineate the scope of theinvention. Its purpose is to present some concepts of the invention in asimplified form as a prelude to the more detailed description that ispresented later.

The present invention is directed generally toward a system, apparatus,and method for reciprocally scanning a workpiece. According to oneexemplary aspect of the invention, a process chamber associated with theion beam is provided, wherein a motor is operably coupled to the processchamber. The motor comprises a rotor and a stator, wherein the rotor andthe stator are each dynamically mounted relative to one another about afirst axis such that the rotor and stator are operable to individuallyrotate and counter-rotate about the first axis. As in the case of atypical motor having a stator and a rotor, an electromagnetic forcebetween the rotor and the stator to generally determine a rotationalposition of the rotor about the first axis. However, in view of thedynamic coupling of the stator relative to the rotor, the stator isoperable to act as a reaction mass responsive to the rotation of therotor, particularly during periodic reversal of the direction ofrotation of the rotor.

According to one exemplary embodiment of the invention, a shaft isfixedly coupled to the rotor, wherein the shaft extends along the firstaxis into the process chamber. A scan arm generally residing within theprocess chamber is operably coupled to the shaft in a radialconfiguration, wherein the scan arm comprises an end effector or otherworkpiece support member for receiving and restraining the workpiece ata distal end of the scan arm. As such, rotation of the shaft causes thescan arm, being generally fixedly coupled thereto, to correspondinglyrotate about the first axis. Rotation of the shaft is selectivelyreversed to generate a swinging motion of the scan arm in a pendulumtype manner, wherein the workpiece is reciprocatingly transported alonga first, generally arcuate, scan path and the rotational position of therotor generally determines a position of the workpiece with respect tothe ion beam along the first scan path. According to another example, acontroller is provided, wherein the controller is operable to controlthe position of the workpiece along the first scan path by controllingthe electromagnetic force between the rotor and the stator.

In accordance with another exemplary aspect of the invention, agenerally constant velocity of the end effector can be maintained in apredetermined range of motion along the first scan path, wherein atranslational velocity of the end effector with respect to a generallystationary reference is controlled, and wherein acceleration anddeceleration of the end effector occurs outside of the predeterminedrange of motion of the end effector.

According to another exemplary aspect of the invention, an inertial massis coupled to the stator, wherein the inertial mass rotates about thefirst axis and generally provides a reversal of direction of rotation ofthe scan arm, and thus, a reversal of direction of the workpiece alongthe first scan path. The inertial mass is further balanced about thefirst axis, wherein a torque in relation to the first axis is generallyminimized. Therefore, the electromagnetic force between the rotor andthe stator is operable to rotate the stator in reaction to anacceleration or deceleration of the rotor, thus generally confininginertial forces to the first axis.

The rotor, stator, and scan arm, according to another example, aregenerally balanced about the first axis, wherein torque associated withthe first axis is generally minimized. One or more counterweights may beassociated with the stator and scan arm, wherein the one or morecounterweights generally balance the respective components about thefirst axis. Furthermore, according to another exemplary aspect of theinvention, the stator comprises an inertial mass coupled thereto,wherein the inertial mass is significantly greater than that of the scanarm, and wherein a force on the stator caused by the oscillation of thescan arm is generally absorbed by the rotation of the inertial mass andthe stator. Still further, a control of the rotation of the scan armabout the first axis by controlling the electromagnetic force betweenthe rotor and the stator is operable to precisely control the rotationof the rotor.

According to yet another exemplary aspect, the motor and associated scanarm are further operable to translate along a second scan path,generally referred to as a slow scan axis, wherein the second scan path,for example, is generally perpendicular to at least a portion of thefirst scan path.

To the accomplishment of the foregoing and related ends, the inventioncomprises the features hereinafter fully described and particularlypointed out in the claims. The following description and the annexeddrawings set forth in detail certain illustrative embodiments of theinvention. These embodiments are indicative, however, of a few of thevarious ways in which the principles of the invention may be employed.Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified perspective view of an exemplary reciprocatingdrive apparatus according to one aspect of the present invention.

FIG. 2 is a cross-sectional side view of an exemplary reciprocatingdrive system according to another aspect of the invention.

FIG. 3 is a partial side view of an exemplary scan arm according toanother exemplary aspect of the invention.

FIG. 4 is a simplified perspective view of another reciprocating driveapparatus according to another aspect of the present invention

FIG. 5 is a block diagram of a method for reciprocating a workpieceaccording to another exemplary aspect of the invention.

FIGS. 6-8 illustrate several views of an exemplary reciprocating driveapparatus according to yet another exemplary aspect of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed generally towards a reciprocatingdrive system, apparatus, and method for reciprocally translating aworkpiece in one or more dimensions. More particularly, thereciprocating drive apparatus is operable to translate the workpiece intwo generally orthogonal dimensions along respective first and secondscan paths with respect to an ion beam, wherein the workpiece may betranslated at a generally constant translational or linear velocity whenbeing subjected to the ion beam. Furthermore, as implied by the term“reciprocating drive apparatus”, the apparatus and method of the presentinvention provide a reciprocating and selectively reversible transportof the workpiece along the first scan path, and is advantageouslyoperable to limit vibration and to optimize control of the reciprocatingor oscillating transport motion of the workpiece along the first scanpath. In particular, the reciprocating drive apparatus of the presentinvention comprises a reaction mass, wherein the reaction mass generallyconfines forces exerted by the reciprocating drive apparatus to theapparatus itself by rotating about a single axis.

In further detail, the reciprocating drive apparatus comprises a motorhaving a rotor and a stator, wherein each of the rotor and stator aredynamically mounted relative to one another about a single axis, andoperable to rotate individually about the single axis. This dynamicmounting configuration and relationship between the stator and rotorpermits rapid acceleration and deceleration of the workpiece at oppositeends of the scan path, wherein a generally uniform translation (e.g.,constant acceleration/deceleration or velocity) of the workpiece can beattained within a predetermined range, and wherein inertial forcesassociated with the translational motion, and particularly forcesassociated with reversal of the scan direction associated with thereciprocating motion of the apparatus, are substantially confined to theaxis of rotation. Accordingly, the present invention will now bedescribed With reference to the drawings, wherein like referencenumerals may be used to refer to like elements throughout. It should beunderstood that the description of these aspects are merely illustrativeand that they should not be interpreted in a limiting sense. In thefollowing description, for purposes of explanation, numerous specificdetails are set forth in order to provide a thorough understanding ofthe present invention. It will be evident to one skilled in the art,however, that the present invention may be practiced without thesespecific details.

Referring now to the figures, in accordance with one exemplary aspect ofthe present invention, FIG. 1 illustrates a simplified perspective viewof an exemplary reciprocating drive apparatus 100 operable toreciprocally translate or oscillate a workpiece 102 along apredetermined first scan path 104. It should be noted that thereciprocating drive apparatus 100 of FIG. 1 is illustrated to provide anupper-level understanding of the invention, and is not necessarily drawnto scale. Accordingly, various components may or may not be illustratedfor clarity purposes. It shall be understood that the various featuresillustrated can be of various shapes and sizes, or excluded altogether,and that all such shapes, sizes, and exclusions are contemplated asfalling within the scope of the present invention.

As implied by the use of the term “reciprocating drive apparatus”, inone example, the drive apparatus of the present invention is operable toreciprocally translate or oscillate the workpiece 102 in a reversiblemotion along the first scan path 104, such that the workpiece translatesalternatingly back and forth with respect to a generally stationary ionbeam 105, wherein the apparatus can be utilized in an ion implantationprocess, as will be discussed hereafter in greater detail.Alternatively, the reciprocating drive apparatus 100 may be utilized inconjunction with various other processing systems, which may includeother semiconductor manufacturing processes such as, for example, astep-and-repeat lithography system (not shown). In yet anotheralternative, the apparatus 100 can be utilized in various processingsystems not related to semiconductor manufacturing technology, and allsuch systems and implementations are contemplated as falling within thescope of the present invention.

According to one aspect of the present invention, the reciprocatingdrive apparatus 100 comprises a motor 106 operably coupled to a scan arm108 wherein the scan arm is further operable to support the workpiece102 thereon. The motor 106, for example, comprises a rotor 110 and astator 112, wherein the rotor and the stator are dynamically coupled andoperable to individually rotate about a first axis 114. The rotor 110 isfurther operably coupled to a shaft 116, wherein the shaft generallyextends along the first axis 114 and is operably coupled to the scan arm108. In the present example, the rotor 110, shaft 116, and scan arm 108are generally fixedly coupled to one another, wherein rotation of therotor about the first axis 114 generally drives rotation of the shaftand scan arm about the first axis, thus generally translating theworkpiece 102 along the first scan path 104. Alternatively, the rotor110, shaft 116, and scan arm 108 may be otherwise coupled to oneanother, wherein the rotation of the rotor and/or shaft may drive alinear translation of the scan arm with respect to the first axis 114,as will be further discussed infra.

Referring now to FIGS. 2 and 6-8, an exemplary reciprocating drivesystem 200 is illustrated in cross-section comprising a reciprocatingdrive apparatus 201, such as the reciprocating drive apparatus 100 ofFIG. 1, wherein the reciprocating drive apparatus may be furtherutilized in an ion implantation process. It will be understood that theexemplary reciprocating drive system 200 of FIG. 2 is operable to scan aworkpiece 202 through an ion beam 205 in two dimensions, as will bediscussed in greater detail hereafter. According to one exemplary aspectof the present invention, the reciprocating drive system 200 comprises amotor 206, such as the motor 106 of FIG. 1, wherein the motor of FIG. 2is operably coupled to a process chamber 208, and wherein the processchamber is further associated with the ion beam 205. The ion beam 205,for example, may comprise a group of ions traveling together alongclose, substantially parallel, trajectories taking the form of a spot orso-called “pencil beam”, as may be formed by any suitable ionimplantation system (not shown) known in the art, the details of whichwill not be discussed here.

According to the present invention, the process chamber 208 may comprisea generally enclosed vacuum chamber 210, wherein an internal environment212 within the process chamber is operable to be generally isolated froman external environment 214 outside the process chamber. For example,the vacuum chamber 210 can be configured and equipped so as to maintainthe internal environment 212 at a substantially low pressure (e.g., avacuum). The process chamber 208 may be further coupled to one or moreload lock chambers (not shown), wherein the workpiece may be transportedbetween the internal environment 212 of the process chamber and theexternal environment 214 without substantial loss of vacuum within theprocess chamber. The process chamber 208 may alternatively be comprisedof a generally non-enclosed process space (not shown), wherein theprocess space is generally associated with the external environment 214.

In one example, the process chamber 208 serves as a generally stationaryreference 216, wherein the process chamber is generally fixed withrespect to the external environment 214. In another example, a processmedium 218, such as the ion beam 205, serves as the generally stationaryreference 216, wherein the process chamber 208 is operable to move withrespect to the process medium. The process medium 218, for example, maybe alternatively associated with other semiconductor processingtechnologies. For example, the process medium 218 may comprise a lightsource (not shown) associated with a lithography process. Accordingly,the present invention contemplates any process chamber 208 and processmedium 218 operable to be utilized in processing the workpiece 202,whether the process chamber be enclosed, non-enclosed, fixed, ortransitory, and all such process chambers and process mediums arecontemplated as falling within the scope of the present invention.

In accordance with another exemplary aspect of the invention, the motor206 comprises a rotor 220 and a stator 222, wherein the rotor and thestator are operable to individually rotate about a first axis 224, andwherein an electromagnetic force (not shown) between the rotor and thestator generally drives a rotation of the rotor about the first axis.For example, a control of the electromagnetic force between the rotor220 and the stator 222 is operable to selectively drive the rotation ofthe rotor in a clockwise or counter-clockwise direction about the firstaxis 224, as will be discussed infra. In another example, the motor 206further comprises a motor housing 226, wherein the motor housing isgenerally stationary with respect to the first axis 224. The motorhousing 226 in the present example generally encases the rotor 220 andstator 222, and further generally serves as the generally stationaryreference 216 for the rotation of the rotor and stator. A least aportion of the rotor 220 and stator 222 generally reside within themotor housing 226, however, the motor housing need not enclose the rotorand the stator. Accordingly, the rotor 220 and the stator 222 areoperable to individually rotate with respect to the motor housing 226,wherein the motor housing is further operable to generally support therotor and the stator therein. It should be noted that while the presentexample describes the motor housing 226 as being the generallystationary reference 216, other generally stationary references may bealternatively defined.

The motor 206, in one example, comprises a brushless DC motor, such as athree-phase brushless DC servo motor. The motor 206, for example, may besized such that a substantially large diameter of the motor (e.g., arespective diameter of the stator 222, and/or the rotor 220) provides asubstantially large torque, while maintaining a moment of inertiaoperable to provide rapid control of the rotation of the rotor. Thereciprocating drive system 200 further comprises a shaft 228 operablycoupled to the motor 206, wherein in one example, the shaft is fixedlycoupled to the rotor 220 and generally extends along the first axis 224into the process chamber 208. Preferably, the rotor 220 is directlycoupled to the shaft 228, as opposed to being coupled via one or moregears (not shown), wherein such a direct coupling maintains asubstantially low moment of inertia associated with the rotor, whilefurther minimizing wear and/or vibration that may be associated with theone or more gears.

According to another example, the process chamber 208 comprises anaperture 229 therethrough, wherein the shaft 228 generally extendsthrough the aperture from the external environment 214 to the internalenvironment 212, and wherein the motor 206 generally resides in theexternal environment. Accordingly, the shaft 228 is operable to rotateabout first axis 224 in conjunction with the rotation of the rotor 220,wherein the shaft is generally rotatably driven by the rotor inalternating, opposite directions. In the present example, the shaft 228may be substantially hollow, thereby providing a substantially lowinertial mass. Likewise, the rotor 220 may be substantially hollow,further providing a substantially low rotational inertial mass.

One or more low-friction bearings 230, for example, are furtherassociated with the motor 206 and the shaft 228, wherein the one or morelow-friction bearings rotatably couple one or more of the rotor 220, thestator 222, and the shaft to a generally stationary reference, such asthe housing 226 or the process chamber 208. The one or more low-frictionbearings 230, for example, generally provide a low coefficient offriction between the respective rotor 220, stator 222, shaft 228, andmotor housing 226. In another example, at least one of the one or morelow-friction bearings 230 may comprise an air bearing (not shown), aliquid field environment, or other bearing known in the art.

In accordance with another exemplary aspect of the invention, thereciprocating drive apparatus 201 is partitioned from the processchamber 208, such that minimum wear and contamination occurs within theinternal environment 212. For example, the shaft 228 is generally sealedbetween the process chamber 208 and the external environment 214 by arotary seal associated with the shaft and the process chamber, whereinthe internal environment 212 within the process chamber is generallyisolated from the external environment.

The reciprocating drive system 200 further comprises a scan arm 232operably coupled to the shaft 228, wherein the scan arm is operable tosupport the workpiece 202 thereon. According to another example, thescan arm 232 comprises an elongate arm 234 extending radially from thefirst axis 224, wherein the elongate arm is generally fixedly coupled tothe shaft 228, wherein the rotation of the shaft about the first axisgenerally translates the workpiece 202 with respect to the first axis.In one example, the scan arm 232 is coupled to the shaft 228 at a centerof gravity of the scan arm, wherein the scan arm is substantiallyrotationally balanced about the first axis 224. In another example, thescan arm 232 is comprised of a light weight material, such as magnesiumor aluminum.

The scan arm 232 may further comprise an end effector 236 operablycoupled thereto, whereon the workpiece 202 is generally supportedthereon. The end effector 236, for example, comprises an electrostaticchuck (ESC) or other workpiece clamping device is operable toselectively clamp or maintain the workpiece 202 with respect to the endeffector. The end effector 236 may comprise various other devices formaintaining a grip of the workpiece 202, such as a mechanical clamp orvarious other retaining mechanisms (not shown) as may be known in theart, and all such devices are contemplated as falling within the scopeof the present invention.

In another example, the scan arm 232 may further comprise acounterweight 238 operably coupled thereto, wherein the counterweightgenerally balances a mass of the scan arm, end effector 236, and theworkpiece 202 about the first axis 224. Such a counterweight 238 mayadvantageously assist in centering the mass moment of inertia of thescan arm 232 about the first axis 224, thus dynamically balancing thescan arm about the first axis. Accordingly, the scan arm 232, shaft 228,rotor 220, and stator 222 are generally dynamically balanced about thefirst axis 224, thus generally eliminating side load forces, other thangravitational forces. The counterweight 238, for example, may becomprised of heavier metal than the scan arm 232, such as steel.

In the case where the reciprocating drive apparatus of the presentinvention is utilized in an ion implantation system, the reciprocatingdrive apparatus 201 may further comprise a load lock chamber (not shown)associated with the process chamber 208, wherein scan arm 232 is furtheroperable to rotate and/or translate the end effector 236 to the loadlock chamber in order to insert or remove workpieces 202 to or from theprocess chamber. Furthermore, a faraday cup 237 is provided within theprocess chamber 208 and positioned within a path of the ion beam 205,wherein the faraday cup is operable to generally sense a beam currentassociated with the ion beam. Accordingly, the sensed beam current canbe utilized for subsequent process control.

According to another exemplary aspect, the end effector 236 may berotatably coupled to the scan arm 232 about a second axis 240, whereinthe end effector is operable to rotate about the second axis. An endeffector actuator 242 may be operably coupled to the scan arm 232 andthe end effector 236, wherein the end effector actuator is operable torotate the end effector about the second axis 240. The second axis 240,for example, is generally parallel to the first axis 224, wherein theend effector actuator 242 may be operable to selectively rotate theworkpiece relative to the ion beam to vary the so-called “twist angle”of implant, as will be understood by those of skill in the ionimplantation art. Alternatively, the rotatable coupling of the endeffector 236 to the scan arm 232 may be utilized to maintain arotational orientation (e.g., a rotational orientation 250 of FIG. 3) ofthe workpiece 202 with respect to the ion beam 205 by continuouslycontrolling the rotation of the end effector 236 about the second axis240. The end effector actuator 242 of FIG. 2 may comprise a motor (notshown) or mechanical linkage (not shown) associated with the scan arm232 operable to maintain the rotational orientation of the workpiece 202with respect to the ion beam 205. Alternatively, the end effectoractuator 242 may comprise a pivot mount (not shown) associated with thesecond axis 240, wherein inertial forces associated with the workpiece202 are operable to maintain the rotational orientation of the workpiece202 with respect to the ion beam 205. Maintaining the rotationalorientation of the workpiece 202 with respect to the ion beam 205 isadvantageous when the ion beam impinges on the workpiece at anon-orthogonal angle (not shown), and/or when a crystalline or otherstructure associated with the workpiece (e.g., a semiconductorsubstrate, or a substrate having structures formed thereon) plays a rolein the uniformity of the ion implantation.

Referring now to FIG. 3 an exemplary rotation 244 of the shaft 228 aboutthe first axis 224 of FIG. 2 is illustrated, wherein the scan arm 232,end effector 236, and workpiece 202 are further rotated about the firstaxis. Accordingly, the workpiece 202 can be reciprocally translatedalong a first scan path 246 with respect to the ion beam 205 (e.g., viaone or more cyclical counter-rotations of the shaft 228 about the firstaxis 224), wherein the ion beam of FIG. 2 is illustrated as going intothe page of FIG. 3. The rotation 244 (and counter-rotation) of the shaft228 about the first axis 224 can be advantageously controlled in orderto oscillate or reciprocate the end effector 236 along the first scanpath 246 in a uniform manner, as will be discussed hereafter. FIG. 3further illustrates a rotation 248 of the end effector 236 about thesecond axis 240 as discussed above, wherein the rotation of the endeffector, and hence, the workpiece 202, about the second axis can befurther controlled in order to maintain the rotational orientation 250of the workpiece with respect to the first axis 224 or ion beam 205(e.g., rotational orientation of the workpiece with respect to the ionbeam is indicated by a triangle 252 that is fixed with respect to theworkpiece).

In order to evenly process the workpiece 202, such as providing an evenimplantation of ions into the workpiece from the ion beam 205, it isimportant to maintain a generally constant translational velocity of theend effector 236 when the workpiece is subject to the ion beam 205 whiletraveling along the first scan path 246. Maintaining a generallyconstant velocity of the end effector 236 while the workpiece passes 202through the ion beam 205, for example, provides a generally uniform doseof ions to the workpiece, thus evenly processing the workpiece as ittravels along the first scan path 246 in a pendulum-type motion.

Therefore, in one embodiment, a generally constant velocity is desiredfor a predetermined scanning range 254 associated with the movement ofthe workpiece 202 through the ion beam 205. The predetermined scanningrange 254 is generally associated with the physical dimensions of theworkpiece 202 (e.g., greater than a diameter D of the workpiece). In thepresent example, the predetermined scanning range 254 is generallydefined by the workpiece 202 traveling a distance greater than a totalof the diameter D of the workpiece plus a width of the ion beam 205,wherein the workpiece travels through the ion beam along the first scanpath 246, and wherein the ion beam is relatively scanned betweenopposite ends 256 of the workpiece.

According to another embodiment, a desired velocity profile for theworkpiece 202 within the predetermined scanning range 254 may bedefined, wherein the desired velocity profile generally depends on aconfiguration of the reciprocating drive apparatus 201. For example,depending on whether the workpiece 202 is fixed or rotatable withrespect to the scan arm 232, a respective generally constant velocity ora variable velocity of the rotation 244 of the scan arm (and thus, arespective generally constant or variable velocity of the workpiecealong the first scan path 246) may be desired. If, for example, theworkpiece 202 is rotated with respect to the scan arm 232 in order tomaintain the rotational orientation 250 along the first scan path 246,the rotational velocity of the scan arm about the first axis 224 may bevaried when the ion beam 205 nears ends 255 of the predeterminedscanning range 254 (e.g., an increase in velocity by about 10% near theends of the predetermined scan range) in order to provide a generallyuniform dose of ions to the workpiece along the curvilinear path. Asanother alternative, or in addition to varying the velocity of the scanarm 232, properties of the ion beam 205, such as the ion beam current,can be varied in order to produce a generally uniform dosage of ions tothe workpiece 202.

As indicated in one of the embodiments above, it is generally desirablefor the workpiece 202 to maintain a substantially constant velocitywithin the predetermined scanning range 254 along the first scan path246 in order to generally evenly expose the workpiece 202 to the ionbeam 205. However, due to the reciprocating, alternatingly reversing,motion of the workpiece 202 along the first scan path 246, accelerationand deceleration of the workpiece is inevitable, such as betweenclockwise and counter-clockwise rotations (e.g., counter-rotations) ofthe shaft 228 about the first axis 224. Therefore, in order toaccommodate acceleration and deceleration of the scan arm 232, endeffector 236, and workpiece 202, a maximum scan distance 258 traveled bythe opposite ends 256 of the workpiece 202 between maximum positions 260and 262 along the first scan path 246 can be further defined, whereinthe acceleration and deceleration can occur in overshoot regions 264,either when the ion beam 205 is not in contact with the workpiece, orwhen at least a portion of the ion beam is not in contact with theworkpiece.

It is important to note that in conventional two-dimensional scanningsystems, a permissible amount of acceleration and deceleration during areversal of workpiece direction is substantially limited in order tominimize inertial forces and associated reaction forces transmitted tothe remainder of the conventional scanning system. However, the presentinvention obviates such limitations, such that inertial forces aregenerally confined to the first axis 224, as will now be discussed ingreater detail.

According to the present invention, rapid acceleration and decelerationof the workpiece 202 within the overshoot regions 264 is attained bygenerally confining inertial forces associated with one or more of theworkpiece, end effector 236, scan arm 232, shaft 228, rotor 220, andstator 222 to the first axis 224. In accordance with one exemplaryaspect of the invention, the stator 222 of FIG. 2, being operable torotate about the first axis 224, is further operable to act as areaction mass 266 to the rotation 244 of the scan arm 232 shown in FIG.3. For example, the reaction mass 266 of FIG. 2 is operable to generallyprovide a rapid acceleration and deceleration of the rotor 220, shaft228, scan arm 232, end effector 236, and workpiece 202, wherein inertialforces associated with the rotation and/or translation of the rotor,shaft, scan arm, end effector, and workpiece are generally translatedinto a rotation of the stator 222 about the first axis 224 by anelectromagnetic force between the rotor and the stator, and wherein theinertial forces are generally balanced and confined to the first axis.Accordingly, torque associated with the rotation of the stator 222 isgenerally confined to the first axis 224, thus vibrationally isolatingor decoupling the forces associated with the reciprocation of theworkpiece 202 along the first scan path 246 from the stationaryreference 216.

Such a confinement of the inertial forces to the first axis 224substantially reduces vibration seen in conventional scanning systems.Accordingly, the stator 222, acting as the reaction mass 266, istherefore operable to accelerate and decelerate the scan 232 arm in theovershoot region 264 of FIG. 3, wherein the electromagnetic forcebetween the stator and the rotor 220 of the motor 206 generallydetermines a rotational position of the respective rotor and the statorabout the first axis. Accordingly, the rotational position of the rotor220 about the first axis 224 generally determines the rotationalposition of the shaft 228, scan arm 232, end effector 236, and workpiece202 about the first axis, wherein the rotational position of the rotorcan be efficiently controlled by controlling the electromagnetic forcebetween the rotor and the stator.

In accordance with another exemplary aspect of the invention, the stator222 (e.g., wherein the stator acts as the reaction mass 266) has asubstantially larger mass moment of inertia than that of one or more ofthe rotor 220, shaft 228, scan arm 232, end effector 236, and workpiece202. According to another example, an inertial mass 268 (e.g., a“flywheel”) is further operably coupled to the stator 222, wherein theinertial mass is further operable to act as the reaction mass 266 inorder to further limit the rotation of the stator in reaction to (e.g.,to counteract) the rotation of the rotor 220, scan arm 232, end effector236, and workpiece 202 about the first axis 224. The inertial mass 268,for example, is generally greater than or equal to the total massmoments of inertia of one or more of the rotor 220, shaft 228, scan arm232, end effector 236, and workpiece 202. In one example, the massmoment of inertia associated with the reaction mass 266 is roughly tentimes greater than a total of the mass moments of inertia of the rotor220, shaft 228, scan arm 232 (and counterweight 238), end effector 236,and workpiece 202, wherein for every ten degrees of rotation of therotor, the stator 222 need only rotate one degree about the first axis224. Providing a substantially large inertial mass 268, for example,further advantageously reduces back-EMF associated with the velocity ofthe rotor 220 relative to the stator 222, thus reducing an amount ofenergy required to drive the motor 206.

In accordance with yet another exemplary aspect of the presentinvention, the motor 206 of FIG. 2, for example, is operable to vary arotational velocity of the shaft 228 (and hence, the translationalvelocity of the workpiece 202) in accordance with the rotationalposition of rotor 220 with respect to the stator 222. In accordance withanother example, the reciprocating drive apparatus 201 further comprisesone or more sensing elements 270, wherein the rotational position 244 ofthe workpiece 202 along the first scan path 246 can be furtherdetermined. For example, the one or more sensing elements 270 of FIG. 2are operable to sense the rotational position of one or more of the scanarm 232, shaft 228, rotor 220, and stator 222 about the first axis 224,wherein the sensed rotational position(s) can be utilized for feedbackcontrol of the translational position of the workpiece 202 as will bedescribed infra. For example, the one or more sensing elements 270 maycomprise one or more high resolution encoders operable to continuouslyor repeatedly provide feedback control of the respective rotationalposition(s) about the first axis. In another example, the one or moresensing elements 270 comprise a first encoder 272 operable to sense arotational orientation of the rotor 220 with respect to the stator 222,and a second encoder 274 operable to sense a rotational orientation ofthe rotor with respect to the stationary reference 216, such as theprocess chamber 208, motor housing 226, ion beam 205, or otherstationary reference with respect to the rotor.

According to another exemplary aspect, the reciprocating drive apparatus201 further comprises one or more stops 276, wherein the one or morestops generally limit the rotation of the stator 222 with respect to themotor housing 226. The one or more stops 276 generally provide avariable amount of rotation of the stator 222 to generally prevent a“runaway” incident, wherein the stator becomes uncontrollable. The oneor more stops 276, for example, comprises one or more adjustablemechanical or electrical limits (not shown) operably coupled to themotor housing 226, wherein the amount of rotation of the stator 222 isgenerally constrained between the stops.

In another aspect of the present invention, the reciprocating driveapparatus 201 is further operable to translate the workpiece 202 along asecond scan path 278, wherein the second scan path is substantiallyperpendicular to at least a portion of the first scan path 246 of FIG.3. For example, the second scan path 278 is substantially perpendicularto the midpoint of the first scan path 246 illustrated in FIG. 3. Thesecond scan path 270 may be achieved by means of a slow scan actuator280, which is further operably coupled to the motor 206, wherein theslow scan actuator is operable to translate one or more of the motor andprocess chamber 208 along a third axis 282 with respect to thestationary reference 216. The third axis 282, for example, is generallyperpendicular to the first axis 224, and is generally parallel to thesecond scan path 278 of the workpiece 202 with respect to the ion beam205.

Thus, it will be understood, that, according to one exemplary aspect ofthe invention, the first scan path 246 is associated with a “fast scan”of the workpiece 202, and the second scan path 278 is associated a “slowscan” of the workpiece, wherein the workpiece may be continuouslytransported along the second scan path as the workpiece reciprocatinglytravels along the first scan path. Alternatively, the workpiece 202 maybe serially indexed an increment of predetermined length along thesecond scan path 278 for every translation of the workpiece betweenmaximum positions 260 and 262 along the first scan path 246 (e.g., asillustrated in FIG. 3). For example, for a full back and forthoscillation cycle or reciprocation of the workpiece 202 along the firstscan path 246, the slow scan actuator 280 will translate the workpiecetwo increments of predetermined length along the second scan path 278. Atotal translation of the motor 206 along the second scan path 278, forexample, is approximately the diameter D of the workpiece 202 in FIG. 3plus the height of the ion beam 205.

The slow scan actuator 280 of FIG. 2, for example, may comprise a servomotor, a ball screw, or other system (not shown), wherein the motorhousing 226 and associated motor 206, and hence, the workpiece 202, canbe smoothly translated along the second scan path 278. Such a slow scanactuator 280, for example, is operable to permit the stationary ion beam205 to “paint” the workpiece 202 residing on the end effector 236 bypassing the workpiece through the ion beam 205 while the end effectoralso travels along an arcuate scan path in cyclical counter-rotations(e.g., oscillation), thus uniformly implanting ions across the entireworkpiece.

The reciprocating drive apparatus 201 may further comprise a dynamicsliding seal 284 (e.g., a sliding bearing seal), wherein the slidingseal substantially seals the internal environment 212 of the processchamber 208 from the external environment 214 (e.g., atmosphere). Forexample, the process chamber 208 may define a slot-shaped aperture 286therethrough and extending generally parallel with the third axis 282,wherein the shaft 228 generally extends through the slot. One or morelinear bearings 288, for example, may be utilized to slidingly couplethe motor housing 226 to the process chamber 208. Accordingly, the shaft228 is operable to translate within the slot 286 in conjunction with thetranslation of the motor 206 along the third axis 282. The sliding seal284 further surrounds the slot-shaped aperture 286 and further generallyisolates the internal environment 212 within the process chamber 208from the external environment 214. Such a sliding seal 284, for example,further generally isolates the scan arm 232 and end effector 236, andpermits the translation of the end effector within the process chamber208 along the second scan path 278, while limiting potential deleteriouseffects caused by moving components associated with the motor 206.Alternatively, any or all of the reciprocating drive apparatus 201 mayreside within the process chamber 208.

According to yet another exemplary aspect of the invention, a frame 290is provided, wherein the frame is generally fixed relative to the ionbeam 205. For example, the frame 290 can be further considered astationary reference 216. In the present example, the process chamber208 may be pivotally coupled to the frame 290 about a fourth axis 292that is generally perpendicular to the ion beam 205, wherein arotational position of the process chamber about the fourth axis furthergenerally defines a tilt angle (not shown) between the ion beam and asurface 294 of the workpiece 202. In another example, the scan arm 232is rotatably coupled to the shaft 228 via a hub 295, wherein the scanarm is further operable to rotate about a fifth axis 296. The fifth axis296 is further generally perpendicular to the first axis 224, wherein arotation of the scan arm 232 about the fifth axis alternatively providesthe tilt angle (not shown) discussed above. The net effect of utilizingthe fourth axis 292 to position the process chamber 208 in combinationwith the rotation of the workpiece 202 about the second axis 240 whilethe scan arm 232 rotates about first axis 224, is to generally sweep theworkpiece through the ion beam 205 while maintaining a fixed tilt andtwist angle of the workpiece relative to the ion beam. Furthermore, sucha combination generally maintains a point of impact of the ion beam 205with the workpiece 202 that is roughly fixed in space, thus generallyensuring that all points on the workpiece are implanted by the beam atthe same angles and with the same beam size.

In accordance with yet another exemplary aspect of the presentinvention, a primary drive actuator (not shown) is operably coupled tothe shaft 228, wherein the primary drive actuator is operable to providea primary rotational force to the shaft. The primary drive actuator, forexample, is operable to further vary the rotational velocity of theshaft 228, in conjunction with the motor 206, wherein the position ofthe workpiece along the first scan path 246 can be further controlled.Accordingly, the motor 206 can generally act as an accelerator anddecelerator for the rotation of the shaft 228, while not substantiallyacting to control the translation of the workpiece 202 within thepredetermined scanning range 254 of FIG. 3.

In accordance with another aspect of the invention, a controller 298 isprovided, wherein the controller is operable to control the position ofthe workpiece 202 along the first scan path 246 by controlling theelectromagnetic force between the rotor 220 and the stator 222. Thecontroller 298, for example, is further operable to control the rotationof the workpiece 202 about the second axis 240 by controlling the endeffector actuator 242. Furthermore, the controller 298 is operable tocontrol the position of the motor 206 along the third axis 282 bycontrolling the slow scan actuator 280. The controller 298, for example,is operable to control the rotational and/or translation position of theworkpiece 202 along the first scan path and second scan path, whereinthe control is based, at least in part on the feedback from the one ormore sensing elements 270.

Furthermore, according to another exemplary aspect of the invention, thecontroller 298 (e.g., a motion controller) is operably coupled to one ormore power supplies, drivers and/or amplifiers (not shown) associatedwith the reciprocating scan apparatus 201, such as the motor 201, one ormore sensing elements 270, end effector actuator 242, and slow scanactuator 280, wherein the controller efficiently controls thereciprocating scan apparatus.

In accordance with another exemplary aspect of the invention, thegeneral scheme of motion control disclosed in the invention generallyprovides a smoothness of motion of the end effector 236 (e.g., aconstant velocity within the predetermined scanning range 254 of FIG.3), and can minimize velocity errors associated therewith. According toanother example, the controller 298 of FIG. 2 comprises a proportionalintegral derivative (PID) control device that can be utilized by thecontroller, wherein the one or more sensing elements 270 providefeedback control.

While the structure and system disclosed in FIGS. 1-3 relate to apendulum type motion, the present invention also contemplates a linearmotion system, wherein a workpiece translates linearly along a firstscan path. For example, FIG. 4 illustrates simplified view of anotherreciprocating drive apparatus 300 operable to reciprocally translate oroscillate a workpiece 302 along a linear first scan path 304. Thereciprocating drive apparatus 300, in one example, is operable toreciprocally translate or oscillate the workpiece 302 along the linearfirst scan path 304 with respect to a generally stationary ion beam 305,wherein the apparatus can be utilized in an ion implantation process.Alternatively, the reciprocating drive apparatus 300 may be utilized inconjunction with various other semiconductor processing systems, such asa step-and-repeat lithography system (not shown). In yet anotheralternative, the apparatus 300 can be utilized in processing systems notrelated to semiconductor technology, and all such systems andimplementations are contemplated as falling within the scope of thepresent invention.

According to one aspect of the present invention, the reciprocatingdrive apparatus 300 comprises a motor 306 operably coupled to a scan arm308 wherein the scan arm is further operable to support the workpiece302 thereon. The motor 306, for example, comprises a rotor 310 and astator 312, wherein the rotor and the stator are operable toindividually rotate about a first axis 314, in a manner similar to thatdescribed above. The rotor 310 is further operably coupled to a shaft316, wherein the shaft generally extends along the first axis 314 and isoperably coupled to the scan arm 308. In the present example, the rotor310 and shaft 316 are generally fixedly coupled to one another, andwherein the shaft and scan arm 308 are in mating engagement with oneanother, wherein the rotation of the shaft is operable to drive a lineartranslation of the scan arm, wherein the first scan path 304 issubstantially linear. According to one example, the scan arm 308comprises an engagement portion 320, and wherein the shaft 316 comprisesa driver portion 322, and wherein the engagement portion of the scan armis operably coupled to the driver portion of the shaft. For example, theengagement portion 320 comprises a rack 324 and the driver portion 322comprises a pinion 326. Alternatively, the engagement portion 320 maycomprise a substantially flat surface (not shown), wherein the driverportion comprises a roller (not shown) operable to engage the engagementportion. It will be understood that any engagement portion 320 anddriver portion 322 operable to linearly translate the scan arm 308 maybe utilized, and all such engagement and driver portions arecontemplated as falling within the scope of the present invention.

According to another exemplary aspect of the invention, thereciprocating drive apparatus 300 further comprises a counterbalance arm328, wherein the shaft 316 and counterbalance arm are further in matingengagement with one another. The counterbalance arm 328, for example,may be diametrically opposed to the scan arm 308 about the shaft 316,wherein the rotation of the shaft is further operable to drive a lineartranslation of the counterbalance arm in a direction generally oppositethat of the scan arm. Such a counterbalance arm 328, for example, mayfurther comprise an inertial mass 330, and further confines inertialforces to the first axis 314. According to another example, thereciprocating drive apparatus further comprises one or more lineartranslation bearings (not shown), wherein the one or more lineartranslation bearings generally confine the translation of the scan arm308 and the counterbalance arm 328 to a linear path.

According to still another exemplary aspect of the present invention,FIG. 5 is a schematic block diagram of an exemplary method 400illustrating the integration and operation of the exemplaryreciprocating drive apparatus of FIGS. 14. While exemplary methods areillustrated and described herein as a series of acts or events, it willbe appreciated that the present invention is not limited by theillustrated ordering of such acts or events, as some steps may occur indifferent orders and/or concurrently with other steps apart from thatshown and described herein, in accordance with the invention. Inaddition, not all illustrated steps may be required to implement amethodology in accordance with the present invention. Moreover, it willbe appreciated that the methods may be implemented in association withthe systems illustrated and described herein as well as in associationwith other systems not illustrated.

As illustrated in FIG. 5, the method 400 begins with providing aworkpiece on a scan arm in act 305, such as the scan arm 232 of FIG. 2.The scan arm is operably coupled to a motor comprising a rotor and astator, and wherein the rotor and stator are operable to individuallyrotate and counter-rotate about a first axis. In act 310, anelectromagnetic force is applied between the rotor and stator, thereintranslating the workpiece through an ion beam along a first scan path.In act 315 a position of the workpiece is sensed, such as sensing arotational position of one or more of the shaft, rotor, and stator aboutthe first axis. In act 320, the electromagnetic force between the rotorand stator is controlled or selectively varied along the first scanpath, and wherein the stator rotates and counter-rotates about the firstaxis in reaction to the reciprocation of the workpiece. The control inact 320, for example, is based, at least in part, on the sensed positionof the workpiece.

In accordance with another exemplary aspect of the present invention,the reciprocating drive apparatus can be further utilized in a processchamber (not shown) that is in a state of high vacuum, wherein nomechanical components such as lubricated bearings or actuators aredirectly exposed to the environment. In order to achieve such ends, thejoints of the apparatus, for example, are further provided with vacuumseals, such as Ferro-fluidic seals. It should be understood that anytype of movable vacuum seal that provides an integrity of cleanliness ofthe process is contemplated as falling within the scope of the presentinvention. Therefore, the present invention is further operable toprovide a motion generation and wafer scanning in a clean, vacuumenvironment.

Although the invention has been shown and described with respect to acertain preferred embodiment or embodiments, it is obvious thatequivalent alterations and modifications will occur to others skilled inthe art upon the reading and understanding of this specification and theannexed drawings. In particular regard to the various functionsperformed by the above described components (assemblies, devices,circuits, etc.), the terms (including a reference to a “means”) used todescribe such components are intended to correspond, unless otherwiseindicated, to any component which performs the specified function of thedescribed component (i.e., that is functionally equivalent), even thoughnot structurally equivalent to the disclosed structure which performsthe function in the herein illustrated exemplary embodiments of theinvention. In addition, while a particular feature of the invention mayhave been disclosed with respect to only one of several embodiments,such feature may be combined with one or more other features of theother embodiments as may be desired and advantageous for any given orparticular application.

1. A reciprocating drive apparatus, comprising: a motor comprising arotor and a stator, wherein the rotor and the stator are operable toindividually rotate about a first axis; a shaft rotatably driven by therotor and extending along the first axis; and a scan arm operablycoupled to the shaft, wherein the scan arm is operable to support aworkpiece thereon, and wherein cyclical counter rotations of the shaftare operable to translate the workpiece along a first scan path, whereinthe stator is operable to act as a reaction mass to the rotation of therotor.
 2. The reciprocating drive apparatus of claim 1, wherein anelectromagnetic force between the rotor and the stator generallydetermines a respective rotational position of the rotor and the statorabout the first axis.
 3. The reciprocating drive apparatus of claim 1,further comprising an inertial mass coupled to the stator, wherein theinertial mass is operable to counteract the translation of the scan armabout the first axis.
 4. The reciprocating drive apparatus of claim 3,wherein a mass moment of inertia of the inertial mass is associated witha total of mass moments of inertia of the scan arm and workpiece.
 5. Thereciprocating drive apparatus of claim 1, wherein the scan arm comprisesan end effector, wherein the workpiece is generally supported by the endeffector.
 6. The reciprocating drive apparatus of claim 5, wherein theend effector comprises an electrostatic chuck.
 7. The reciprocatingdrive apparatus of claim 5, wherein the end effector is pivotallymounted to the scan arm, wherein the end effector is operable to rotateabout a second axis generally parallel to the first axis.
 8. Thereciprocating drive apparatus of claim 7, further comprising an endeffector actuator operably coupled to the end effector and the scan arm,wherein the end effector actuator is operable to rotate the end effectorabout the second axis.
 9. The reciprocating drive apparatus of claim 1,further comprising a slow scan actuator operably coupled to the motor,wherein the slow scan actuator is operable to linearly translate themotor along a third axis generally perpendicular to the first axis,therein scanning the along a second scan path.
 10. The reciprocatingdrive apparatus of claim 1, wherein the motor comprises a brushless DCmotor.
 11. The reciprocating drive apparatus of claim 1, wherein themotor is operable to drive the counter-rotations of the shaft withsubstantially constant velocity.
 12. The reciprocating drive apparatusof claim 1, wherein the stator is operable to act as a reaction mass tothe rotation of the rotor and translation of the scan arm and workpiece.13. The reciprocating drive apparatus of claim 1, further comprising aprocess chamber, wherein the shaft extends through an aperture in theprocess chamber, wherein the scan arm generally resides within theprocess chamber and the motor generally resides outside the processchamber, and wherein a rotary seal is provided at an interface betweenthe shaft and the aperture.
 14. The reciprocating drive apparatus ofclaim 1, further comprising one or more sensing elements operable tosense a rotational position of one or more of the shaft, rotor, andstator about the first axis.
 15. The reciprocating drive apparatus ofclaim 14, wherein the one or more sensing elements comprise a firstencoder operable to sense a rotational orientation of the rotor withrespect to the stator and a second encoder operable to sense arotational orientation of the rotor with respect to a generallystationary reference.
 16. The reciprocating drive apparatus of claim 14,wherein the one or more sensing elements comprise one or more highresolution encoders associated with one or more of the shaft, rotor, andstator.
 17. The reciprocating drive apparatus of claim 1, wherein theshaft is substantially hollow.
 18. The reciprocating drive apparatus ofclaim 1, wherein the scan arm is fixedly coupled to the shaft, andwherein the first scan path is curvilinear.
 19. The reciprocating driveapparatus of claim 1, wherein the shaft and scan arm are in matingengagement with one another, wherein the rotation of the shaft isoperable to drive a linear translation of the scan arm, and wherein thefirst scan path is substantially linear.
 20. The reciprocating driveapparatus of claim 19, wherein the scan arm comprises an engagementportion, and wherein the shaft comprises a driver portion, wherein theengagement portion of the scan arm is operably coupled to the driverportion of the shaft, and wherein the rotation of the shaft drives thelinear translation of the scan arm.
 21. The reciprocating driveapparatus of claim 20, wherein the engagement portion comprises a rackand the driver portion comprises a pinion.
 22. The reciprocating driveapparatus of claim 20, wherein the engagement portion comprises asubstantially flat surface, and wherein the driver portion comprises aroller.
 23. The reciprocating drive apparatus of claim 19, furthercomprising a counterbalance arm, wherein the shaft and counterbalancearm are further in mating engagement with one another, wherein thecounterbalance arm is diametrically opposed to the scan arm about theshaft, and wherein the rotation of the shaft is operable to drive alinear translation of the counterbalance arm in a direction generallyopposite that of the scan arm.
 24. The reciprocating drive apparatus ofclaim 23, further comprising one or more linear translation bearings,wherein the one or more linear translation bearings generally confinethe translation of the scan arm and the counterbalance arm to a linearpath.
 25. The reciprocating drive apparatus of claim 19, furthercomprising one or more linear translation bearings, wherein the one ormore linear translation bearings generally confine the translation ofthe scan arm to a linear path.
 26. A method for reciprocating aworkpiece, the method comprising: providing the workpiece on a scan arm,wherein the scan arm is operably coupled to a motor comprising a rotorand a stator, and wherein the rotor and stator are operable toindividually rotate and counter-rotate about a first axis; and applyingan electromagnetic force between the rotor and stator, thereintranslating the workpiece along a first scan path.
 27. The method ofclaim 26, further comprising: sensing a position of the workpiece; andcontrolling the electromagnetic force between the rotor and stator toreciprocate the workpiece along the first scan path, wherein the controlis based, at least in part, on the sensed position of the workpiece, andwherein the stator rotates and counter-rotates about the first axis inreaction to the reciprocation of the workpiece.
 28. A method forreciprocating a workpiece, the method comprising: rotating a rotor of amotor about a first axis, therein translating the workpiece along afirst scan path; and rotating a stator of the motor about the first axisin reaction to the rotation of the rotor.
 29. The method of claim 28,further comprising: sensing a rotational position of the rotor and thestator; and controlling the rotation of the rotor, wherein the controlis based, at least in part, on the sensed rotational position of therotor and the stator.
 30. The method of claim 28, further comprisingtranslating the workpiece along a second scan path, wherein the secondscan path is generally perpendicular to at least a portion of the firstscan path.